1. Technical Field
The present invention relates to plotters and similar devices employing a medium upon which plots are made and, more particularly, to a method of differentiating between an end-of-roll marker on a roll of media and a back edge of a cut sheet of media and associated apparatus wherein the method comprises the steps of, marking an end-of-roll position on rolls of media with a hole of diameter "d"; moving media between optical sensing apparatus directing a light beam through the media at a point on a path followed by the hole of roll-fed media being employed; detecting light not intercepted by media being employed at a point along the media; moving the media along the path a distance greater than "d"; setting an end-of-roll marker sensed condition if no light is now detected; and, setting a back edge of cut sheet sensed condition if light is now detected.
2. Background Art
Plotting devices such as pen plotters normally operate in one of two modes as far as the plotting media employed therein. As depicted in FIG. 1, there can be a plotting bed 10 having a plotting apparatus 12 positioned above it. A single cut sheet 14 of the plotting media 16 can be moved over the plotting bed 10 for plotting upon by the plotting apparatus 12. In the alternative, as depicted in FIG. 2, the plotting media 16 can be provided on a roll 18 from which a portion for plotting is cut each time by a cutting mechanism (not shown). In prior art plotters, the user must inform the plotter logic not only whether cut or roll sheet media is being used; but, in addition, the size of the media upon which to plot.
An objective of most modern plotting devices is to have them as self-sufficient as possible. That is, the operation of the plotting device should be as transparent as possible to the user. The term "user friendly" is more than a catch phrase in modern technology as exemplified by video cassette recorders (VCRs) and the complaints made against them for their complexity of programming and use for time shifted recording. Users of plotters, computers, VCRs, and other devices do not want to have to learn complex procedures in order to use the device for its intended purpose. When it comes to plotting devices in particular, the user does not want to have to input operating parameters such as whether the plotter is presently using roll paper or cut paper and plotting size. Ideally, the plotter itself should determine such facts and set its associated internal parameters accordingly.
It is common in contemporary plotting devices to provide one or more optical sensors to determine the edges of a sheet of plotting media 16 loaded for use. That way, the side edges and front and back edges can be located. By knowing the distance moved between these points, the logic of the plotter can easily determine the length and width of a known cut sheet. The problem comes in determining the back edge when it is not known whether cut sheet or roll-fed media is being employed.
Wherefore, it is an object of this invention to provide a way of automatically determining whether cut sheet media or roll-fed media is being employed in a plotting type device.
It is another object of this invention to provide a way of determining the back edge location of a plotting media whether cut sheet media or roll-fed media is being employed.
It is still another object of this invention to automatically set the plotting size to use as a function of the length and width of the paper sensed without regard as to whether cut sheet media or roll-fed media is being employed.
Other objects and benefits of the invention will become apparent from the description and figures which accompany it.